Batteries are commonly used in a wide array of applications and for a variety of vehicles such as boats, motor homes, fork lifts, and others. In most cases, the batteries used in such applications may be charged, discharged, and recharged again. In this manner, a single battery may serve as a source of electrical current for a significantly long period of time.
Although a battery may be charged and discharged many times, inefficient use of the battery can significantly shorten the battery's life. In general, a battery's service life is determined by the number of times a battery may be charged and discharged. One charge and discharge of a battery constitutes a single battery cycle. Thus, each battery has an expected lifetime that is limited to a given number of cycles. Improper battery cycling procedures can severely limit a battery's life. Perhaps most importantly, discharging the battery to extremely low voltages can damage the battery, reducing the battery's expected lifetime. Additional factors such as temperature, storage periods, discharge loads, and others may further reduce the battery's expected lifetime.
Without knowledge of battery state-of-charge and history such as the time since last charge, total number of cycles, time since last equalization, and total discharge time, battery users are generally unable to obtain efficient battery usage. Inevitably, batteries will be discharged to dangerously low levels, equalized at random times, and experience lifetimes many cycles shorter than that expected of an efficiently maintained battery.
Moreover, the lack of information about battery state-of-charge and history can result in wasted employee hours. Many industrial battery users for devices such as forklifts commonly remove the batteries from the devices to recharge them. Without information regarding the battery's current state-of-charge, battery-operated devices frequently discharge the battery to the point at which the battery is dead. In addition to discharging the battery to a harmfully low level, the battery often dies when the device is at an inconvenient location for removal and replacement of the battery. Furthermore, industrial batteries are often charged at a common charging station at which there may be dozens of batteries in various states of charge or discharge. In many such cases, there is no way to ascertain the number of cycles experienced by each battery, or whether a given battery has recently been discharged, charged, or equalized. As a result, a dead battery may be replaced by a battery having a less than optimal state-of-charge.
Worse yet, batteries may be discharged to a dangerously low level. When multi-cell series-connected batteries are discharged to a sufficiently low end voltage, it is possible for the poorest cell in the battery to be driven into voltage reversal. In some cases, this could result in cell venting or rupture.
In order to maximize battery life, and avoid the hazards associated with dangerous charge or discharge levels, it would be beneficial to have an inexpensive battery monitoring system that could be quickly and easily installed on a battery to provide "at-a-glance" status and key historical information about how the battery has been used.
Devices presently available to provide battery monitoring information are less than adequate. In some cases, batteries are manufactured with simple charge indicators. Generally, such indicators provide information related to the battery state-of-charge on a display that allows a battery user to determine whether the battery's charge is low, medium, or high. Even where such integrated battery monitors provide more detailed information regarding the battery's state-of-charge, they do not indicate other key historical information such as the number of cycles, lifetime discharge time, time since last charge, time since last equalization, and others.
Others have attempted to address this problem by providing a battery-mountable monitor capable of counting the number of charge cycles. For example, U.S. Pat. No. 5,136,620 to Eaves discloses a device which counts the number of charge cycles accumulated on a particular battery by sensing and counting each reversal of electrical current flow. Unfortunately, the device disclosed by Eaves is expensive and requires the installation of a specially configured intercell connector with an integral shunt and electronics. Moreover, the Eaves device is prone to registering erroneous cycle counts. This is likely to occur, for example, during the battery charging process. During the battery charging process, a charging system may charge to a particular voltage level and then cease charging. Once the discharge current reduces the battery's voltage to a sufficiently low level, the charger will begin charging again to return the battery to a fully charged level. Because the current will have been reversed, this trivial discharge and charge process will be counted by current-sensing devices such as the Eaves device as one charge cycle. In a worst case, the battery monitor could record many charge cycles during a single battery charging operation.
In addition to the less than ideal operation of the presently available battery monitoring devices, the devices that are presently available do not provide easy-to-read, "at-a-glance" displays. Presently, battery monitoring devices either provide little information, are difficult to read at a glance, or both.
Finally, other battery monitoring devices that are available and provide detailed information typically are not battery-mountable. In many cases, such devices are designed for use in conjunction with a battery charging system and are therefore intended to reside with the battery charger rather than the battery. While such devices may be capable of providing information about certain battery characteristics, and may even have a user-friendly display, they provide no information at the point at which they are most necessary--on the battery and the device to which it is connected.
The present invention is directed to providing a battery monitoring unit that overcomes the above-mentioned problems.